6-8 speed freewheel replacment?

[lar49]

Is it possible to replace a 6 speed freewheel with an 8 speed freewheel and maintain the same hub width? I understand that there will be other components to change along with this.

[waynemyer]

No.  At the very least, you will need to add spacers to the drive side of the hub and re-dish the wheel.  Unless you are a lightweight rider and/or using a Phil hub, it is inadvisable to make the jump to 8-speed.  The greater width of the freewheel and its inboard mounting point (the threads) make for a much longer moment arm with which the freewheel can act on the hub.  Most hubshells cannot stand up to that stress, especially for loaded touring.  Additionally, the bearings are more inboard, placing more stress on the axle.

You mention that there would be other corollary component changes.  If you really want 8-speed, you are much better off making the jump to cassettes.  It's really a much better system, especially for loaded touring and greater gear numbers.

[whittierider]

I would echo that.  Axles occasionally broke with 5-speed-- not very often, but it became more and more often as more and more freewheel speeds (6, then 7, then 8) made the right-side wheel bearings get farther and farther from the dropout.  The industry's answer was to go to a freehub where the ratchet mechanism (ie, the "clicker") was in essence part of the hub instead of the stack of cogs, and put the right-side bearings in the freehub body, much closer to the dropout, and slide the cassette over it.  The only bearings in the hub shell are in the left side, while the freehub body has the right-side bearings.

[DaveB]

I would echo that.  Axles occasionally broke with 5-speed-- not very often, but it became more and more often as more and more freewheel speeds (6, then 7, then made the right-side wheel bearings get farther and farther from the dropout.  The industry's answer was to go to a freehub where the ratchet mechanism (ie, the "clicker") was in essence part of the hub instead of the stack of cogs, and put the right-side bearings in the freehub body, much closer to the dropout, and slide the cassette over it.  The only bearings in the hub shell are in the left side, while the freehub body has the right-side bearings.

All true and a good summary.  I'd add that the switch from 5-speed freewheels(120 mm rear dropout spacing) to 6/7-speed freewheels (both use 126 mm dropout spacing) did indeed increase the frequency of broken axles and/or required better quality axle material to survive. 

By the time 8-speed arrived (130 mm dropout spacing) the freewheel design was beyond it's limit and 8-speed freewheels, while available, are rare and never caught on.  By then, the freehub had pretty much taken over as it is an inherently superior and stroger design.

Phil Wood does offer freewheel hubs in 130 mm spacing that will accept 8-speed freewheels but these are quite expensive and get by by using superior, and expensive, axles.  At this point, they are a novelty rather than a mainstream product. 

[Westinghouse]

Some of the five-sprocket freewheels I've seen were no wider than six-speed freeweels. The five-sprocket FWs had their sprockets spaced wider apart, and the six-speed FWs were spaced closer, but, of course, with enough clearance for the chain to function properly. Lay them down flat one aside the other, and you will see they are the same width / height or however you look at it.

[DaveB]

Some of the five-sprocket freewheels I've seen were no wider than six-speed freeweels. The five-sprocket FWs had their sprockets spaced wider apart, and the six-speed FWs were spaced closer, but, of course, with enough clearance for the chain to function properly. Lay them down flat one aside the other, and you will see they are the same width / height or however you look at it.

What you appear to be describing were known as "Ultra 6" freewheels which had the cogs spaced closer together and fit in the same hub and dropout width as a standard 5-speed.  AFAIK, Sun Tour was the only maker of these freewheels and generally they shifted poorly.  They also required a narrower chain than 5-speed freewheels.

Standard spaced 6-speed freewheels were indeed wider than 5-speeds and used 126 mm dropouts to keep the rear wheel dish within reasonable limits.  When 7-speed freewheels came along, the cogs were spaced similar to an Ultra-6 so they also fit in 126 mm dropouts and, again, required a narrow chain.